The chemical vapor deposition (CVD) method and the atomic layer deposition (ALD) method are methods in which a film is formed or deposited using two or more gases such as a material gas and a reactive gas (support gas) and the like. In a film-forming apparatus for carrying out the above methods, if the material gas and the reactive gas get mixed before they are introduced into the film-forming space, there will occur CVD reaction (film-forming reaction). In order to prevent the reaction from taking place, it must be so arranged that the material gas comes into contact with the other gases only when the material gas is introduced into the film-forming space through a shower head structure. As an apparatus to meet such conditions, there is known a film-forming apparatus in which a material gas diffusion chamber and a reactive gas diffusion chamber are independently disposed by separately defining into sections inside the shower head such that each gas is introduced into the film-forming space through the shower head structure without mixing gases (see, e.g., Patent Document 1).    Patent Document 1: JP-A-2005-129712 (FIG. 1, paragraphs 0017, etc.).